Capillary mercury switches



Jan. 18, 1966 N. BERMAN CAPILLARY MERCURY SWITCHES 3 Sheets-Sheet 1Filed March 14, 1962 INVENTOR.

NELSON HERMAN Jan. 18, 1966 N. BERMAN 3,230,333

CAPILLARY MERCURY SWITCHES Filed March 14, 1962 3 Sheets-Sheet 2 Fig.4?

I HYDROGEN 3 GAS United States Patent C 3,230,333 CAPILLARY MERCURYSWITCHES Nelson Ber-man, 6 Magnolia Drive, New Hyde Park, N.Y. FiledMar. 14, 1962, Ser. No. 179,727 7 Claims. (Cl. 200-152) The presentinvention relates to improvements in mercury switches, relays, and othercontact making devices.

In particular, it relates to mercury switches employing closed capillarytubes.

Hermetically sealed gas filled mercury switches are widely used forswitching electrical circuits because the use of liquid contact surfacesresults in long troublefree operation, freedom from electrical noise, nocontact bounce, and low contact resistance.

The use of many mercury switches is limited to applications where theyare always in a vertical or near vertical position, and where they arenot subject to shock or vibration. Other switches of the type in which asolid dielectric separates a single pool of mercury into two pools whenthe circuit is opened do not have consistently high insulationresistance in the open circuit condition.

The objects of this invention are as follows:

(1) To provide an improved mercury switch which can be operated in anyposition.

(2) To provide a mercury-switch which is unafiected by shock andvibration.

(3) To provide a switch which can be operated rapid- 1y.

(4) To provide a hermetically sealed gas filled mercury switch which canbe made in a very small size.

The invention will be more fully described with reference to theaccompanying drawings. In the drawings:

FIG. '1 is a longitudinal section of a capillary mercury switch.

FIG. 2 is a longitudinal section of a normally open, panel mounted,capillary mercury switch.

FIG. 3 is a longitudinal section of a normally closed, panel mounted,capillary mercury switch.

FIG. 4 is a longitudinal section of a panel mounted relay including acapillary mercury switch.

FIG. 5 is a longitudinal section of a multiple tube capillary mercuryswitch.

FIG. 6 is a longitudinal section of a tubular diaphragm capillarymercury switch.

FIG. 7 is a plan view of a rotary cornmutating switch includingcapillary mercury switches.

FIG. 8 is a sectional view taken on line 88 of FIG. 7.

FIG. 9 is a longitudinal section of a multiple circuit capillary mercuryswitch.

FIG. 10 is a schematic of a crossbar matrix switch.

FIG. 11 is an electrical connection chart for the matrix switch of FIG.10.

FIG. 12 is a longitudinal section of a magnet-ostriction capillarymercury relay.

Referring to FIG. 1, this embodiment of the invention is a normally openpush button switch. It is comprised of a glass capillary tube 1interposed between a bellows 2 and a metal capillary tube 3, and asecond glass capillary tube 4. The capillary bore 5, of the metal. tube3 is axially aligned with the bores 6 and 7 of the glass tubes and thediameters of the three tubes are essentially equal. The end of the glasstube 4 is closed. The glass tubes are attached to the metal tube and tothe bellows by the glass to metal seals 8 and 9 respectively.

The end of the bellows away from the glass tube is also closed. Most ofthe volume of the bellows 2 is occupied by a cylindrical rod fillerpiece 10 made of a "ice material inert to mercury such as Teflon. Thefiller piece 10 has small projections 11 at the end adjacent to theglass capillary tube 1 so that the flow of mercury in and out of thecapillary tube 1 is not impeded. The remaining volume of the bellows 2and part of the volume of the glass capillary bore 7 are occupied bymercury 12. The remainder of the glass bore 7, all of the met-a1capillary bore 5, and all of the glass capillary bore 6 are filled witha compressed gas, preferably hydrogen. The leads 13 and 14 are attachedby solder 16 to the metal tube 3 and bellows 2 respectively.

In operation, the electrical circuit including the battery 17 and load18 is completed by deflecting the bellows 2 decreasing internal volumeof the bellows and forcing some of the mercury through the glass tube 1and through the metal tube 3 into the glass tube 4. In order to keep thecontact resistance low the bellows 2 and metal tube 3 are mad-e of amaterial that can be wetted 'by mercury, such as nickel.

T he elements are so proportioned that the end of the a mercury columnis in a glass segment of the capillary channel in both the on and offpositions. This precaution is taken to prevent malfunction of the switchunder conditions of shock, vibration, or acceleration. In the offcondition of the switch, a malfunction can i occur only if the mercurymoves along the tube until it forms a conducting path between the metaltube 3 and the bellows 2. Since the mercury does not wet the glass,capillary force and surface tension of the mercury tend to keep themercury in a single mass. Movement of the mercury mass along thecapillary channel is prevented by the pressure of the gas in the spaceunoccupied by mercury. In the on condition of the switch, malfunctioncan occur only if the mercury column is disrupted. Disruption can occuronly if a portion of the mercury moves along the capillary channel awayfrom the bellows. Again, such movement is prevented by the combinationof capillary force, surface tension and gas pressure.

In the configurations shown in FIGURES 1, 2, 3, 4, 5, 6, and 9, theinvention incorporates a resilient member for changing the sealed volumeof the switch. As shown, the portion of the switch undergoing the changein volume has a volume much greater than the volume of thecapillarychannel. In order to prevent the device from behaving like a thermometerwhen temperature changes occur, a filler piece (10 in FIG. 1) whichreduces the net volume is enclosed in the chamber of the resilientmember. This filler piece could be eliminated by reducing the size ofthe resilient member to capillary dimensions. However, the constructionshown is preferred for ease of mechanical operation and fabrication.

FIGURE 2 shows an embodiment of the invention which includes provisionfor mounting the switch of FIG. 1 in a panel. All of the elements of theswitches shown in FIG. 1 and FIG. 2 are the same except that a bushing19 having a flange 20 and an external thread 21 upon which is threadedthe mounting nut 22 is interposed between the glass capillary tube 1 andthe bellows 2. External circuit connections are made to the lead 23 andthe bushing 19. The switch is a normally open push-button type operatedby finger pressure on the bellows 2.

FIGURE 3 shows an embodiment of the invention which is a normally closedpush button type switch. This embodiment is the switch shown in FIG. 2modified by the addition of a mechanism which changes it from beingnormally open to being normally closed.

The bushing 24 corresponds to bushing 19 of FIG. 2, modified by theaddition of a threaded shank 25 at the bellows end on which is screwedthe cylinder 26 having an internal thread 27. Mounted in the cylinder bymeans of a pin 28 is a lever 29. Spring 30, positioned by spacer 30a,acts in combination with lever 29 to keep the bellows deflected untilthe button is depressed. The button 31 and spring 30 and spacer 30:: areretained in the cylinder 26 by the lip 32 formed by spinning over theedge of the cylinder 26. The switch is shown in the normally closedposition with the mercury column 12 completing the circuit between themetal capillary tube 3 and the bushing 24.

An embodiment of the invention in the form of a relay is shown in FIGURE4. The bushing 24 in FIG. 2 is replaced by bushing 33. This bushing hasbeen counterbored to allow for recessed mounting of the capillary tubes.The bushing 33 has a threaded shank 34 at the bellows end on which ismounted the internally threaded cylindrical cap 35. Within the cap arethe relay actuating elements, coil 36, armature 37, and spring 38,which, in conjunction with the switch capsule 39, operate in theconventional fashion as a normally closed relay. External connections tothe relay coil 36 are made to the leads 40. The load circuit isconnected to the lead 41 and the bushing 33.

In this invention the electrical circuit is completed by the mercury ina capillary channel. This channel can have dimensions equivalent to acircular diameter of from .005 to .040" with a preferred dimension about.010". This small diameter limits the amount of current which can behandled in a single contact making element. FIGURE shows an embodimentof the invention which provides multiple parallel paths for the current,thus increasing the amount of current which can be handled. In FIGURE 5a single metal bellows 42 is sealed to the ceramic case 43. Shown in thecase are four capillary elements 44 comprised of a metal capillary tube45 between and in axial alignment with two glass capillary tubes 46 and47. One end of the capillary element 44 is closed. The other end opensinto the chamber formed by the bellows 42. The metal capillary tubes areconnected to the lead 48 by solder 49. The lead 48 passes through thecase 43 in a ceramic to metal seal 50. The capillary elements 44 areembedded in plastic 51 to improve the mechanical strength of the switch.

A filler piece 52 is contained in the bellows 42 to reduce the netvolume of the bellows. The remainder of the bellows 42 is filled withmercury 53 and the mercury extends partially into the bore of the glasscapillary tubes adajcent to the bellows. The remainder of the capillaryelements 44 are filled with compressed gas, preferably hydrogen.External connections are made to the leads 48 and 48a. The switch isoperated by deflecting the bellows 42.

FIGURE 6 shows another embodiment 55 of the invention. This differs fromthe embodiment shown in FIG- URE 1 in that a thin Walled resilient metaltube 54 is substituted for the bellows 2 of FIGURE 1. This switch isoperated by applying pressure to the sides of the thin walled tube 54.The configuration of the other parts of the switch shown in FIGURE 6differ somewhat from those shown in FIGURE 1 but there are no otherfunctional differences.

The switch 55 shown in FIGURE 6 is used as the contact making element ofthe rotary commutating switch shown in FIGS. 7 and 8. In this embodimentof the invention the switches 55 are located in grooves in the baseplate56. A flexible arm 57, loaded by the spring 58, is attached to the shaft59 of the motor 60. A roller 61 is mounted in the end of arm 57 by pin62. Operation of the motor causes the arm 57 to rotate and the roller 61applies pressure to the resilient tube 54 of the switch 55 as it passesover the switch. Hence as the arm rotates the switches 55 aresequentially momentarily operated. The load connections to the leads 63of the individual switches and the operation of the commutator switchfor sampling signals from multiple external sources can be made invarious ways well known to the art.

Another embodiment 64 of the invention is shown in FIG. 9. In thisembodiment the switch shown in the first embodiment, FIG. 1, is modifiedby the addition of multiple alternate conducting and non-conductingcapillary tube segments. In FIG. 9, the bellows 2, filler piece 10,glass capillary tube 1, and metal capillary tube 3, are the same asthose shown in FIG. 1. The additional glass capillary tubes, 65, 66, 67,and the additional metal capillary tubes 68, 69, and 70, are joinedtogether in axial alignment alternating a conducting with anon-conducting segment. The last segment is the closed end glasscapillary tube 4. External leads 71 to 75 inclusive are connected to thebellows 2 and to the metal tubes. Two masses of mercury are contained inthe switch. One 76 fills the bellows and extends into the glasssegment 1. The other mercury mass 77 is entirely in the capillarychannel 78 completley filling the segments, 68, 66, and 69, andextending partially into the glass segments, 65 and 67. The normalminisci positions are L, M, and N in FIG. 9. The portions of thecapillary channel not occupied by mercury are filled with hydrogen.

Upon actuation of the switch, mercury 76 is displaced into the capillarychannel 58. This movement of mercury compresses the gas between the twomasses of mercury 76 and 77. The increased pressure causes the secondmass 77 to move along the tube until the pressures in the two gas filledsections are equal. The amount of displacement of the two masses ofmercury is controllable by the dimensional design of the bellows 2 andcapillary segments. In the embodiment shown in FIGURE 9, after actuationone mass of mercury 76 completely fills the bellows 2, the glass segment1, and the metal segment 3;

and partially fills the glass segment 65. The other mass 7 ConditionNormal Actuated Closed. Open. Open. Closed.

It will be obvious to those skilled in the art that various otherswitching functions can be performed by proper selection of the numberof capillary segments, amount, number and position of the mercurymasses.

FIGURE 10 shows schematically the construction of a matrix switch usingpluralities of switches similar to the multiple segment switches ofFIGURE 9 and constructed and wired as shown. A rectangular array of anysize is made by orienting the switches as shown and soldering themetallic segments 79 together at the points of intersection 82.Actuation of any two of the bellows 2 will complete a circuit. Thepositions of the mercury columns in metallic segments 81 prior toactuation is indicated at 80 in FIG. 10. After actuation the mercurycolumn 80 forms a conducting path between metallic segments 81 and 79.FIG. 11 is a tabulation of some of the connections that can be made byactuation of two of the switches (1) to (8). g

Another embodiment of the invention is a relay utilizing themagnetostriction effect for displacing mercury. Certain metals have theproperty of changing their dimensions when magnetized. For example,iron-cobalt alloys will change longitudinally up to 96 parts permillion. Electrostrictive materials such as barium titanate change theirdimensions when subjected to an electrostatic field.

The manner in which the magnetostriction effect is utilized is describedreferring to FIGURE 12. A compartment is formed by two coaxialconcentric shells 87 and 88, each having one end open. Anelectromagnetic coil 84 enclosed in a case 83 made of magnetostrictivematerial, preferably an alloy of iron and cobalt is located in and fillsthe peripheral compartment between the two shells 87 and 88. One end ofthe case 83 is sealed by the welds 94 to the plate 85. The ends of thecoil 84 are attached to the insulated feed-through glass-to-metal-sealedterminals 86 which are located in plate 85. The plate 85 is also sealedby the welds 95 to the shells 87 and 88. A capillary switch capsule 89is sealed by the Weld 92 in an opening in the center of the closed endof the inner shell 88. The open end of the capillary channel connects tothe chamber 97 formed by the shells 87 and 88 and one end of the case83. The chamber 97 is filled with mercury 91 and the mercury extendsinto part of the capillary channel 96. Foam rubber 90 fills theremainder of the space in shell 88.

When the coil 84 is energized it sets up an electromagnetic field whichmagnetizes the case 83. The length of the case increases and mercury isforced out of the chamber 97 into the capillary channel 96. While theamount of dimensional change due to magnetostriction is small, in thisinvention the dimensional change is, in effect, hydraulically amplifiedby an amount equal to the ratio of the area of the end of the case 83 tothe area of the capillary channel 96. This ratio will vary with thedesign parameters chosen. However, a preferred and easily obtained ratiois 2,000 to 1. The variation of length of the mercury column in theclosed capillary channel 96 is utilized in the manner described for theother embodiments of the invention, to open and close the circuitbetween the leads 93.

While a relay employing a magnetostriction element has been describedthis element can be replaced by an electrostrictive element, such asbarium titanate without departing from the scope of this invention.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to preferredembodiments, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in the artwithout departing from the spirit of the invention. It is the intention,therefore, to be limited only as indicated by the scope of the followingclaims.

What is claimed is:

1. A switching device including in combination a capillary tubecomprising an electrically conductive section and a nonconductivesection, a variable volume reservoir, a supply of conductive fluid insaid reservoir, said fluid supply comprising a portion of said fluidextending into said capillary tube and a solid slug of inert materialhaving a low thermal coeflicient of expansion disposed in saidreservoir.

2. A switching device including in combination a capillary tubecomprising an electrically conductive section and a nonconductivesection, a supply of conductive fluid comprising a portion extendinginto said capillary tube and magnetostrictive means acting on said fluidto move said portion between a position at which it contacts saidconductive section and a position at which it is out of contact withsaid conductive section.

3. A switching device including in combination a capillary tubecomprising an electrically conductive section and a nonconductivesection, a supply of conductive fluid comprising a portion extendinginto said capillary tube and electrostrictive means acting on said fluidto move said portion between a position at which is contacts saidconductive section and a position at which it is out of contact withsaid conductive section.

4. A switching device including in combination a capillary tubecomprising an electrically conductive section and a nonconductivesection, a variable volume reservoir connected to said capillary tube, asupply of conductive fluid in said reservoir and comprising a portion ofsaid fluid extending into said capillary tube, said reservoir beingformed at least in part of maignetostrictive material and means applyinga magnetic fieid to said magnetostrictive material to vary the volume ofsaid reservoir to move said extending portion of said fluid between aposition at which it is out of engagement with said conductive portionand a position at which it is in engagement with said conductiveportion.

5. A switching device including in combination a plurality of capillarytubes each comprising an electrically conductive section and anonconductive section, respective variable volume reservoirs each havinga deformable wall connected to said capillary tubes, respective suppliesof conductive fluid in said reservoirs, each of said fluid suppliescomprising a portion of said fluid extending into its associatedcapillary tube, means mounting said tubes in spaced relationship andmovable means acting on said reservoir walls sequentially to move therespective fluid portions between positions at which they contact theassociated conductive sections and positions at which they are out ofcontact with said conductive sections.

6. A switching device including in combination a capillary tubecomprising a plurality of conductive sections separated by nonconductivesections, means closing an end of said tube, a variable volume reservoirconnected to the other end of said tube, a supply of conductive fluid insaid reservoir, said supply comprising a portion extending into saidcapillary tube, a discrete charge of conductive fluid separate from saidsupply disposed in said tube and gas filling the remainder of said tube,said reservoir being adapted to be actuated to move said extending fluidportion and said discrete fluid portion relative to said conductivesections whereby connections are selectively made and broken to saidconductive sections in response to actuation of said reservoir.

7. A switching matrix including in combination a plu rality of lines andcolumns of intersecting capillary tubes, each of said tubes comprisingconductive and nonconductive sections, respective supplies of conductivefluid connected to the ends of said tubes, said supplies comprisingportions of said fluid extending into said tubes, respective discretecharges of conductive fluid separate from said supplies disposed in saidtubes, gas filling the remainders of said tubes and means acting on saidfluid in said tubes selectively to interconnect predetermined conductivesections.

References Cited by the Examiner UNITED STATES PATENTS 1,680,400 8/1928Ulrey et a1. 200-112 X 2,472,082 6/ 1949 Armstrong 200122 2,566,3699/1951 Putman ZOO-81.6 X 2,587,482 2/1952 Keller 200-87 2,621,26812/1952 Lindstrom et al 20081.6

KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT K. SCHAEFER, BERNARD A. GILHEANY,

Examiners.

1. A SWITCHING DEVICE INCLUDING IN COMBINATION A CAPILLARY TUBECOMPRISING AN ELECTRICALLY CONDUCTIVE SECTION AND A NONCONDUCTIVESECTION, A VARIABLE VOLUME RESERVOIR, A SUPPLY OF CONDUCTIVE FLUID INSAID RESERVOIR, SAID FLUID SUPPLY COMPRISING A PORTION OF SAID EXTENDINGINTO SAID CAPILLARY TUBE AND A SOLID SLUG OF INERT MATERIAL HAVING A LOWTHERMAL COEFFICIENT OF EXPANSION DISPOSED IN SAID RESERVOIR.